1. Field of the Invention
The present invention relates to a document carrying apparatus applicable to an image forming apparatus, typically, a copying machine or a facsimile.
2. Description of Related Art
There are image forming apparatuses such as a copying machine, a facsimile, and the like that comprise a document carrying apparatus which automatically carries a plurality of documents to a document reading portion. The document carrying apparatus separates a document located at the uppermost position of documents piled up on a document placement tray one after another and carries them. Image data on a surface of a document is read by a document reading portion, then, the document is delivered to a document delivery tray disposed at the downstream end of a document carrying passage.
During the time when a document is carried on a platen glass of the document reading portion, image data on the surface of the document is read by a reading unit disposed under the platen glass. Therefore, through the document reading portion, a document must be carried in a suitable carrying state making a contact with the platen glass. Examples of such document carrying apparatuses that improve the document reading performance of the document reading portion can be seen in Japanese Patent Nos. 3499193, 3585723 and JP-A-2004-61978. The document carrying apparatuses described in these patent documents are each disposed facing the platen glass of the document reading apparatus and include a reading guide member that guides a document in such a manner that the document comes into contact the platen glass.
In the automatic document carrying apparatuses described in Japanese Patent No. 3499193 and JP-A-2004-61978, the reading guide member is disposed rotatably in a vertical plane on the pivot shaft that is arranged on the upstream side in the document carrying direction and has the axis extending in the direction perpendicular to the document carrying direction. Thus, the document carrying state at the document reading portion can be stabilized. However, distortion can occur in the vertical direction and the document carrying direction in the reading guide member that is pivotally supported in such state. Accordingly, there is a possibility that the distance between the reading guide member and the platen glass changes from place to place, that is, becomes narrow at a place and wide at another place, and the position of a document with respect to the platen glass cannot be set precisely. And, it is high in the possibility that the document carrying passage deviates from its usual position on the front side and the rear side of the document carrying apparatus.
In the document reading apparatus (the document carrying apparatus) described in Japanese Patent No. 3585723, the reading guide member is supported by a hole having a diameter larger than the pivot shaft that extends in the direction perpendicular to the document carrying direction so that the reading guide member can be moved in the document carrying direction and the vertical direction. Accordingly, it is possible to precisely set the position of a document with respect to the platen glass by disposing the reading guide member along the positioning guide member arranged on the side of the platen glass. However, on the other hand, a deviation can occur in the positional relationship between the reading guide member and the other carrying guide members on the upstream and downstream sides in the document carrying direction of the reading guide member, thereby the document carrying space can change in size and shape. During the time when a document is carried, such a positional deviation of the reading guide member and a change in the document carrying passage caused by the positional deviation can put a burden on the guide member and the document to fluctuate the document carrying speed. Consequently, the document carrying state becomes unstable and a defective image appears.
Besides, as in the above-mentioned document carrying apparatuses described in Japanese Patent No. 3499193 and JP-A-2004-61978, there is a possibility that the document carrying passage changes on the front and rear sides of the document carrying apparatus. Such a trouble can cause not only a change in the length of the document carrying passage for the document carriage and a deviation from perpendicularity but also a problem with an image such as a defective magnification between the front side and the rear side of the document carrying apparatus.